Crystal Growth Process Research Articles

Host Compound DED: Guest Accommodation Type, Noncovalent Host···Guest Interactions, Crystal Densities, and Thermal Stabilities Ensure High Host Selectivities for 4-Methylanisole in Anisole and Methylanisole Mixtures

trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (DED), dimethyl trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylate (H1), and trans-α,α,α′,α′-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol (H2) formed complexes with anisole (ANI) and 2-, 3-, and 4-methylanisole (2-, 3-, and 4-MA) in single-solvent recrystallization experiments. DED was observed to possess an overwhelming selectivity for 4-MA when recrystallized from equimolar binary, ternary, and quaternary mixtures (82.2–99.3%) and nonequimolar binary solutions where this guest species was present. It was therefore demonstrated that DED may serve as an efficient host compound for the separation and purification of many of the mixtures employed in this investigation; extremely high K values (K is a measure of the selectivity of the host compound) were calculated in many instances (137.9, 190.7). However, the selectivity behavior of H1 and H2 in analogous experimental conditions could not be established owing to the extremely slow (months) crystal growth process from these mixtures. Single-crystal X-ray diffraction (SCXRD) experiments revealed that 4-MA interacted with DED via two short stabilizing (host)C–O···π(guest) contacts (3.2782(17), 3.3780(17) Å, 145, 138°). This interaction type was absent in 2(DED)·3-MA and weaker in 2(DED)·2-MA (and only one interaction of this kind was present in the latter complex). Additionally, the crystal density of 2(DED)·4-MA (1.335 g·cm–1) was greater than those of 2(DED)·3(ANI) (1.277 g·cm–1), 2(DED)·2-MA (1.257 g·cm–1), and 2(DED)·3-MA (1.283 g·cm–1), alluding to a tighter packing in the complex with the preferred guest species owing to the shorter contacts in this crystal. The higher density was also explained by a significantly shorter intermolecular (host)π···π(host) interaction in the 4-MA-containing complex. Furthermore, 4-MA experienced more constricted channel accommodation compared with ANI, 2- and 3-MA. Finally, 2(DED)·4-MA possessed the greater thermal stability (the onset of the guest release process, Ton = 101.8 °C) compared with 2(DED)·3(ANI) (unstable at room temperature), 2(DED)·2-MA (Ton = 90.4 °C), and 2(DED)·3-MA (Ton = 85.3 °C).

Study of Copper Electrodeposition at a Very Low Temperature near the Freezing Point of Electrolyte

At or above room temperature, metal electrodeposits often feature coarse grains, uneven microstructure and high roughness with abnormal bulges. In this study, copper electrodeposits with abnormal properties were prepared in a sulfate bath at a low temperature near the freezing point of the electrolyte. The results showed that the average grain size of the copper featured an "increase-decrease" trend while decreasing the temperature form 5 °C to -5 °C, yielding a trend from 0.25 μm to 1 μm and then to 0.6 μm. In the early stage, the temperature does not change the three-dimensional continuous nucleation mode of deposited copper. When the nucleus density reaches saturation, the polarization caused by overpotential will act on the respective nucleation and crystal growth process twice, and finally exhibit a completely different trend than that at room temperature. This study may provide insights for breakthroughs in material properties from a temperature perspective.

Nonisothermal crystallization kinetics of potassium chloride produced by stirred crystallization

The elucidation of the crystal nucleation and growth process can help control crystal size and quality. Here,the classical theory of primary nucleation was first used to study the homogeneous and heterogeneous nucleation mechanism of potassium chloride (KCl) crystallization. The growth kinetics in the presence of seed in KCl was then investigated. To understand the nucleation mechanism of KCl, the induction period of KCl was analyzed using classical nucleation theory to calculate the interfacial tension (γ) and various nucleation parameters, including the radius of the critical nucleus (r*), the critical free energy of the nucleus (ΔG*), and the molecular number of the critical nucleus (i*). The results showed a homogeneous nucleation mechanism at high supersaturation ratios (≥1.10) and a heterogeneous nucleation mechanism at low supersaturation ratios (<1.08). Meanwhile, the KCl crystal exhibited a continuous growth mechanism as inferred by the surface entropy factor (f) value. The SEM data demonstrated that the increase in crystallization temperature and supersaturation ratio could increase the average crystal size. The particle size-independent growth model is suitable for the growth process according to the relationship between crystal particle number density and particle size. In addition, the crystal nucleation and growth rates in stirred crystallization were calculated using the population balance equation, and then various kinetic parameters were estimated. The estimated parameters suggested an increase in growth with an increase in supersaturation ratio and stirring rate. Meanwhile, the impact of each parameter in the nucleation rate equation showed that the degree of influence is suspension density, supersaturation ratio, and finally, stirring rate.

The Impact of BiF3 Doping on the Yb3+ to Yb2+ Reduction during the LiYF4:Yb3+ Crystal-Growth Process

Here, we report on the opportunity to suppress Yb3+ to Yb2+ dopant-ion reduction in LiYbxY1−xF4 mixed crystals during growth processes, using the Bridgmen–Stocbarger technique in graphite crucibles in vacuum. This was carried out by the additional doping of the LiF-YF3-YbF3 powder mixture with 1% of BiF3 additive. The crystals of LiY0.8Yb0.2F4 and LiY0.8Yb0.2F4 with BiF3 doping in the charge, were grown. The spatial distribution of the spectral-kinetic properties of Yb3+ and Yb2+ ions along the grown crystalline-boules were studied. It was established that the Yb2+ concentration rises during the LiY0.8Yb0.2F4 crystal-growth processes without the BiF3 additive: the absorption coefficient of Yb2+ (π-polarization) at 340 nm rises from 0 (at the beginning of the boule) to 2.5 cm−1 (at the end of the boule). In contrast, the undetectable absorption of Yb2+ along the crystals grown from the BiF3 doped melt was displayed. The luminescence-decay time of Yb3+ decreases from 3.7 to 1.8 ms from the beginning to the end of the LiY0.8Yb0.2F4 boule grown from the BiF3 undoped melt, and stays constant (~3.7 ms) along the samples grown with BiF3. Here we demonstrate a positive effect of BiF3 doping on the optical homogeneity of LiYF4:Yb3+ crystals.

In situ TEM observation of liquid flow induced dense phase formation and anisotropic nanocrystal growth

The nucleation and growth of crystals from solutions are fundamental to materials synthesis and its applications. The mass transfer at micro/nano region in solution will greatly influence the crystal growth process, however, to our knowledge, there is rarely research at this scale due to the technique limit. By using in situ liquid cell transmission electron microscopy (TEM), we observed the crystal growth at flow condition with high resolution in real time. Interestingly, we found a flow induced formation of the solute rich dense liquid phase near surface at ultra-low precursor concentration, which then transformed to nanocrystals. The dendritic crystal growth was accelerated by the dense phase droplet merging and the anisotropic crystal growth was controlled by dense phase shape evolution. Our study deepens the understanding of crystal growth mechanisms, which is crucial to determine reaction dynamics and design hierarchical nanomaterials.

Recycled concrete fine powder (RFP) as cement partial replacement: Influences on the physical properties, hydration characteristics, and microstructure of blended cement

Construction and demolition (C&D) waste has caused various economic, environmental, and social problems. This paper investigates the potential of recycled concrete fine powder (RFP) as a supplementary cementitious material. The effect of RFP with different replacement levels on the properties of cement and the mechanism of action were explored from the physical characteristics, mechanical properties, hydration kinetics, hydration products, and pore structure. In this study, scanning electron microscopy, Energy Dispersive X-Ray Spectroscopy, X-ray diffraction, X-ray fluorescence, Thermogravimetric analysis, and Isothermal calorimeter were applied. The results showed that RFP (less than 30%) shortened the setting time and improved the fluidity of cement. The early compressive strength increased by 17.62% of the cement mortar with 10% RFP. When the RFP content was 10%, the flowability of the blended slurry (175.5 mm) increased by 8.0% compared to the pure cement (162.5 mm). With the RFP content increase of the blended cement, the hydration induction period was prolonged, and the peak hydration exothermic rate and the accumulated heat release showed an apparent decreasing trend. The reaction rate of the nucleation and crystal growth (NG) process was much higher than that of the interface (I) and diffusion (D) processes. The low field nuclear magnetic resonance (NMR) technique revealed that RFP filled the large and medium pores of the mortar. The non-destructive layered scanning found that the pores were distributed mainly in the central zone and had a gradient distribution law of gradually decreasing from the middle area to the edge area. Visual analysis of the dynamic distribution of water molecules in the pores and the non-homogeneous characterization also demonstrated the good filling effect of RFP on the mortar. Therefore, RFP can be used as an economical and environmentally friendly cement mixing material to replace partial cement and contribute to reducing carbon emissions in the construction industry.

Precursor solution chemistry via water additive enabling CZTSSe solar cells with over 12% efficiency

High-quality absorber films are imperative for highly efficient Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. Precursor solution chemistry, interconnected with thin-film nucleation and the crystal growth process, should be studied insightfully. Thus, creative rationales and strategies could be proposed to improve the absorber quality, carrier characteristics, and hence device performance. However, the research on precursor solution chemistry in CZTSSe solar cells is still in its infancy. In this study, a facile eco-friendly additive strategy is reported to tailor the 2-methoxyethanol-based CZTS precursor solution chemistry. Incorporating water additives improves the homogeneity and thermogravimetric characteristics of a precursor solution by adjusting the particle sizes and coordination behavior inside the precursor solution. After the tailoring of the precursor solution chemistry, CZTSSe absorbers with high quality are fabricated. Hence, benefiting from the carrier dynamics enhancement, a CZTSSe device with a certified power conversion efficiency of 12.07% is achieved. The results open an avenue in precursor solution chemistry regulation through the use of eco-friendly additives to design highly efficient kesterite CZTSSe solar cells.

A novel nucleation-induced crystallization process towards simultaneous removal of hardness and organics

The co-existence characteristics of saline and organics in industrial effluents complicates their removal by conventional methods. In this study, a novel nucleation-induced crystallization process (NICP) is proposed for the simultaneous removal of organics and hardness ions, and the subsequent densification of the final product. The pre-dosed seed provides reaction sites for the lattice ions, thus inducing the Ca2+/Mg2+ ions to adhere to the seed surface in the form of CaCO3 and Mg(OH)2 by adjusting the pH value. Moreover, organics attach to the seed surface through the coprecipitation and surface complexation in the crystal growth process. Aromatic and carboxyl groups can be considered as reaction sites for organics removal. Hydraulic regulation can accelerate the mass transfer of crystal growth, thus increasing the size of the nucleating pellet. Due to the presence of organics on the growth site of the Ca/Mg crystals, the nucleation pellet surface contains large amounts of functional groups, which enhances the surface complexation with organics. Furthermore, the removal efficiency is improved by the multi-stage NICP, e.g., the removal rates of total hardness and chemical oxygen demand (COD) can achieve 65.63 % and 42.95 % via the 3rd-stage NICP, respectively.

Nanoscale crystal growth processes triggered by captured solid impurity particles

Atomic force microscopy (AFM) was used to study the influence of solid neutral particles on dynamics and kinetics of surface growth on nanoscale. The experiment involved real-time observations of the hydroxymethylquinoxalinedioxide (C10H10N2O4) surface capturing micrometer tourmaline particles of no particular shape and with low adhesiveness to the material of the host crystal. It was made possible to visualize in detail a hillock formation on a screw dislocation triggered by a captured particle, as well as dislocation propagation through the overgrowing macrostep.Out of the multitude of similar size particles, only one of them generated a long-term screw dislocation – that was the particle in whose area a Frank-Read dislocation had been triggered even before the particle cavities were sealed. A detailed scanning showed that the wellknown phenomenon of a dislocation propagating through the overgrowing layers manifests itself as creation of a new screw hillock with monomolecular steps exactly above the lower hillock axis.The author’s method of statistical processing of AFM data was used to compile an array of average tangential and average normal growth rates and their fluctuations. In spite of the matter in the solution not being refilled, the normal and tangential rates showed constant and significant increase.The results were compared with the data from several earlier experiments with and without special impact during the growth process. It was established that the growth rate in the experiment with incorporation of impurities has small and almost stable fluctuations just like in the experiments without any impact.

Stimuli-Responsive Star Polymer as an Admixture for Crystallization of Hollow Crystals.

Polymers are becoming a very popular tool in the crystallization of different compounds. In this work, a new method of crystallization is proposed using stimuli-responsive star polymer in order to obtain hollow structure crystals. In these experiments, amphiphilic copolymer of acrylic acid (AA) and methyl acrylate (MA) were used for isohydric crystallization via they cooling of KCl in deionized water solution. The experiments were realized in quartz cuvette with a magnetic stirrer using a specialized spectrometer with precise temperature control. The crystallization course was monitored by the absorbance readings and analysis of the nucleation energetic effect. It was proved that the moment of the polymer's phase transition occurrence had an important role in the crystal growth process. On the other hand, the occurrence of phase transition did not trigger the nucleation. The supercoolings achieved in the presence of the polymer were significantly higher compared to pure salt crystallization. On the basis of analysis of Particle Size Distribution (PSD) and Critical Aggregation Concentration (CAC) of the polymer, it was proposed that the hydrophobic particles of macromolecules created from polymeric aggregates served as templates for the formation of hollow crystals. Their purity was verified using thermogravimetric analysis (TGA), 1H NMR, and XRD. Only trace amounts of polymer were found in the crystalline product.

Effect of HF, H2SiF6, and Al3+ ions on the crystal growth process and morphology of α-type hemihydrate calcium sulfate in phosphoric acid solution

The reaction of calcium dihydrogen phosphate solution with sulfuric acid in the presence or absence of HF, H2SiF6, and Al3+ ions was used to simulate the crystal growth process of α-type hemihydrate calcium sulfate (α-HH) with 30% P2O5 at a reaction temperature of 95 °C. The changes in Ca2+ ion concentration in the solution were measured at different reaction times. Then, the growth rates and reaction steps of α-HH crystals were fitted using the crystal growth kinetic equation. The growth morphologies of α-HH crystals were characterized using scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectrometry, and differential scanning calorimetry, and the influence mechanism of HF, H2SiF6, and Al3+ ions on the crystal growth process of α-HH were deeply investigated. Results show that the addition of HF, H2SiF6, and Al3+ ions decreased the growth rate constants of α-HH. Without HF, H2SiF6 and Al3+ ions, the growth rate constants of α-HH was 0.7452 × 10−3 (mol·min−1·m−2). When 0.060 mol·L−1 HF was added, the growth rate constants of α-HH decreased to 0.4954 × 10−3 (mol·min−1·m−2). When 0.015 mol·L−1 Al3+ ions and 0.060 mol·L−1 HF were added, the growth rate constants of α-HH decreased to 0.4548 × 10−3 (mol·min−1·m−2). The inhibition of α-HH growth by HF, H2SiF6, and Al3+ ions can be ranked as follows: HF, H2SiF6, and Al3+ ions > HF and Al3+ ions > H2SiF6 > HF. The reaction steps of α-HH in phosphoric acid solution in the presence or absence of HF, H2SiF6, and Al3+ ions were close to 2, and the growth of α-HH crystals was mainly affected by surface diffusion, adsorption, and helical growth mechanism. HF, H2SiF6, and Al3+ ions inhibited the growth of α-HH crystals along the C-axis, resulting in a decrease in aspect ratio, and the morphology of α-HH crystals is short columnar. These impurity ions decreased the intensity of diffraction peaks and crystallinity of the (200), (310), and (400) crystal planes of the α-HH crystals.

Synergistic enhancement of efficiency and stability of perovskite solar cells via dual interface modification

In perovskite solar cells (PSCs), rapid charge transfer at the interfaces between photoactive layer and charge transport layers is very important. Various defects and energy barriers at the interfaces will lead to non-radiative recombination of charge carriers in the charge transfer process, which is not conducive to charge collection and eventually hinder the improvement of power conversion efficiency (PCE) and stability of PSCs. Herein, we report a dual interface modification strategy by using different phosphonic acid molecules to modify the interface between SnO2 layer and perovskite layer and the interface between perovskite layer and hole transport layer, respectively. Acidic diphenylphosphinate chloride (DPC) with UV resistance is employed to modify SnO2 surface before depositing perovskite layer to alleviate the corrosion of OH− in SnO2 to perovskite film and regulate the crystal growth process of perovskite. Methyldiphenylphosphine oxide (MPO) that can coordinate with Pb2+ is used to post-treat the surface of perovskite film to passivate defects at the film surface and grain boundary. The effects of organic interface modifiers on charge transport and charge recombination are comprehensively studied by photoluminescence spectra and electrical measurement. The optimal FA0.85Cs0.15PbI3 device with active area of 0.255 cm2 obtained a PCE of 23.37 %. In addition, the device with working area of ​​1 cm2 achieved the best PCEs of 20.29 %. More interestingly, owing to the strong ultraviolet light absorption ability of DPC, the final device with the dual interface modification can still maintain 91.4 % of the initial efficiency after 1000 h in air and 87.8 % when placed in AM1.5G light for 500 h.

Dual-Emitting Ratiometric Luminescent Thermometers Based on Lanthanide Metal-Organic Complexes with Brønsted Acidic Ionic Liquids.

By introducing Brønsted acidic ionic liquids (ILs), two dual-emitting lanthanide metal-organic complexes (Ln-MOCs) of {[Ln(imdc)(CH3OH)(H2O)3]Cl2}n (LnIMDC, Ln = Eu and Tb, imdc = 1,3-bis(carboxymethyl)imidazolium ion) were first prepared under solvothermal conditions. The crystal structures of LnIMDC were measured by single-crystal X-ray diffraction, and the crystal growth process of LnIMDC was carefully studied. It is found that the crystals are three-dimensional supramolecular structures built up by Ln-O coordination bonds and supramolecular forces. In the temperature range of 303-403 K, LnIMDC show good temperature-dependent emission properties with maximum relative thermal sensitivities of 3.29% K-1 at 375 K and 2.08% K-1 at 303 K for EuIMDC and TbIMDC, respectively. It is worth mentioning that both EuIMDC and TbIMDC exhibit good linear ratiometric emission-temperature response in temperature ranges of 353-403 and 323-373 K, respectively, which render EuIMDC and TbIMDC good ratiometric thermometers in high temperature range. Computational studies on the energy level of ILs [H2imdc]Cl and [imdc]- ion were performed, which validated the high energy transfer efficiency between the [imdc]- and Ln3+ ions and the unique solution concentration- and wavelength-dependent fluorescence properties of [H2imdc]Cl. The high fluorescence performance opens up new opportunities for practical applications of ILs in optical sensing.

β-Ga2O3 bulk single crystals grown by a casting method

A novel casting method was developed to grow β-Ga2O3 bulk single crystals without using a seed crystal. After separation from the crucible and processing, 2-inch diameter single crystal β-Ga2O3 ingots with (100) plane could be obtained and no large imperfection were observed. The 10 × 10 mm2 β-Ga2O3 single crystals samples with different crystal orientation have good crystal quality with full width at half maximum less than 50″, surface roughness less than 0.5 nm and defect density at the magnitude of 104 cm−2. On the basis of the experimental phenomena, a numerical simulation model was proposed to explain the crystal growth process in the casting method.

Natural Amino Acid Enables Scalable Fabrication of High-Performance Flexible Perovskite Solar Cells and Modules with Areas over 300 cm2.

Upscaling large-area formamidinium (FA)-based perovskite solar cells (PSCs) has been considered as one of the most promising routes for the commercial applications of this rising photovoltaics technology. Here, a natural amino acid, phenylalanine (Phe), is introduced to regulate the nucleation and crystal growth process of the large-scale coating of FA-based perovskite films. Better film coverage and larger grain sizes are observed after adding Phe. Moreover, it is found that Phe can effectively passivate defects within perovskite films and suppress the nonradiative recombination due to the strong interaction with under-coordinated Pb2+ ions in the perovskite films. Rigid PSCs based on the blade-coated perovskite films containing Phe obtain a champion efficiency of 21.95%. The corresponding unencapsulated devices also exhibit excellent ambient stability, retaining 95% of their initial efficiencies after storage in the glovebox at 20°C for 1000h. Further, the strategy is applied to fabricate flexible PSCs and modules on polyethylene terephthalate/indium doped tin oxide substrates via slot-die coating. Phe modified flexible devices achieve outstanding efficiencies of 20.21%, 12.1%, and 11.2% with aperture areas of 0.10, 185, and 333cm2 , respectively. The strategy here has paved a promising way for the large-scale production of flexible PSCs.

Kinetic properties of solventing out crystallization of ammonium bicarbonate in a novel ammonia carbon capture system

The novel ammonia carbon capture system of carbonated solvent solventing out crystallization process, the crystal regeneration instead of rich liquid regeneration, to achieve the reduction of regeneration energy consumption. The enhanced crystallization by solventing out method requires the control of crystal yield as well as grain size, and the exploration of the kinetics of solventing out crystallization of carbonated solvent becomes necessary. The crystals produced by solvation crystallization are mainly ammonium bicarbonate, so this paper focuses on the crystallization kinetics of ammonium bicarbonate under different working conditions are studied by the intermittent dynamic method. The kinetic model of the crystal under the working conditions study in this paper is determined by calculation. The growth kinetic model of crystal nucleation rate versus growth rate is shown in Eq. B0=2.994 × 108G1.907. Finally, the integrated rate equations of the crystallization process under different working conditions are derived from the experimental data. The results show that an increase in supersaturation promotes the nucleation rate directly. The stirring rate has positive and negative effects on the crystal growth process. The effect on the nucleation rate is significant when the drop acceleration rate of the solubilizer is high. Under the action of the static magnetic field, by changing the hydrogen bonds in water molecules, the viscosity of water and the surface tension of solution is reduced so that the diffusion process of solute is accelerated and the crystal growth is facilitated. The addition of ammonia, ammonium carbamate and crystalline seeds influence the crystallization process mainly by affecting the supersaturation of the solution. In turn, the width of the metastable zone width is regulated to avoid explosive nucleation and to maintain typical nucleation and growth of the crystallization process.

Simulation of flow field in silicon single-crystal growth using physics-informed neural network with spatial information

Melt convection plays a crucial role in the growth of silicon single crystals. In particular, melt flow transfers mass and heat, and it may strongly affect the crystal growth conditions. Understanding and controlling convection remains a significant challenge in industrial crystal production. Currently, numerical methods such as the finite element method and the finite volume method are mainly used to simulate melt convection in the crystal growth process. However, these methods are not suitable for most applications with real-time requirements. Physics-informed neural networks (PINNs) have the advantages of fast calculation and wide application. They provide a new concept for the numerical solutions of nonlinear partial differential equations (PDEs). This paper proposes a PINN with spatial information to solve the silicon melt flow model, which does not depend on any simulation data. As the network depth (number of layers) increases, the derivative information in the PDE loss becomes weak, which reduces the expression of the original features in the loss function. Therefore, this study introduces spatial information into the hidden layer of the network, thereby enhancing the correlation between the network and the original input and improving the expression ability of the network. Specifically, silicon melt flow models under three rotating conditions are considered. Compared with other methods, the proposed algorithm can accurately capture regions with complex local morphology. The experimental results reveal the flow characteristics of the silicon melt and confirm the effectiveness of the proposed algorithm. All codes and data attached to this manuscript are publicly available on the following websites: https://github.com/callmedrcom/SIPINN.

Control of growth interface shape during InGaSb growth by vertical gradient freezing under microgravity, and optimization using machine learning

The growth of high-quality InGaSb crystals by Vertical Gradient Freezing (VGF) under microgravity was numerically simulated. Machine learning tools were used to optimize the growth conditions. The study focuses on controlling growth interface shape which directly affects the quality and homogeneity of the grown crystals. Initially, Bayesian optimization was utilized to search for the most favorable growth conditions that promote a desirable flatter growth interface shape. Afterward, a reinforcement learning model was developed. The system was subjected to a lower temperature gradient near the feed crystal and to crucible rotation with a rate ranging according to the obtained optimal strategy. Results showed that the interface deformation is considerably reduced, and a flatter growth interface could be maintained. The growth rate and solute concentration uniformity were also improved. This adaptive control recipe proves to hold great potential in the continuous and rapid optimization of other crystal growth processes.

Massive reorientations of bulk single and oligocrystals via solid state processing

Single crystalline materials have the potential to exhibit superior performance because they exclude grain boundaries, which increase susceptibility to creep, oxidation, and corrosion, and make thermal and electronic transport inefficient. However, single crystal properties vary significantly with crystallographic orientation, making the ability to control the orientation critical for their use in applications. The complex nature of crystal nucleation and growth processes makes such control challenging. Here we report a new crystal reorientation mechanism that results in abrupt and massive orientation changes in bulk single crystalline and oligocrystalline alloys via solid state thermal processing. We demonstrated this method in two alloy systems, FeMnAlNi and CuAlMn, and achieved repeated, massive orientation changes in the solid state. These findings offer a new strategy for manipulating the orientation of large single crystals on demand in order to take advantage of their superior and highly anisotropic properties.

Application of optical velocity measurements including a novel calibration technique for micron-resolution to investigate the gas flow in a model experiment for crystal growth

An important step in the fabrication of many modern semiconductor materials and devices is the crystal growth process. These processes take place in high-temperature furnaces using inert gas and other atmospheres. The flow in the gas phase influences the transport of crystal components, dopants and impurities and hence has a significant impact on the grown crystals. In this work, we study the flow in a simplified model of a crystal growth furnace. This model is made of PMMA filled with a Diesel mixture as a model fluid to match the refractive index of PMMA and to allow for measurements in the complex geometry. The comparability to the flow in a real furnace is ensured by matching the Reynolds number. Two optical measurement methods, Particle Image Velocimetry (PIV) and the Laser Doppler Velocity Profile Sensor (LDV-PS) are used to investigate the global flow field as well as the small-scale flow structures. A calibration model is developed for the LDV-PS to reduce systematic measurement errors caused by the refractive index of the model fluid from up to 1% to less than 0,1%. The results obtained in this study improve the understanding of the gas flow behavior inside a crystal growth furnace and provide reference data for simulation. The first analysis shows a highly unsteady flow with unexpected flow direction along the crystal and melt surfaces. The near-surface flow patterns are of particular relevance in crystal growth because of their large influence on the local heat and mass transport during the crystallization process.